As it is well known, low weight premature new-borns require many therapeutic interventions aimed to stabilise and ensure their main vital functions, particularly respiration.
In fact, respiratory insufficiency is the most frequent reason of morbidity and mortality of these young patients.
Treatment of medium-serious level respiratory insufficiency in premature new-borns is realised sustaining the spontaneous respiratory activity of the patient by the use of an automatic ventilator, apparatus able to deliver intermittent positive pressures (+10, +25 cm H2O), with an air and oxygen flow with variable concentration (Intermittent positive Pressure Ventilation: IPPV).
Respirator is provided with a specific ventilation circuit and connection between said circuit and the patient respiratory system is realised by a tube of suitable material and dimensions. Said tube is then fixed in such a way that its distal end is positioned within tertius medius of infant trachea. Thus, a closed pneumatic system is created, permitting transmission of pressure waves generated by the respirator at the patient respiratory system.
In the last decade, clinical research has clearly demonstrated that, among the main factors of the pathogenesis of acute and chronical lesions of a still developing respiratory system of these patients, it is necessary considering included:
1. lack of synchronism between mechanical cycles delivered by the respirator and the patient spontaneous respiratory activity (e.g. coincidence of mechanical inspiration and spontaneous expiration, with high pressures within the respiratory system).
2. prolonged presence of the tracheal tube since it creates lesions and infections.
These two problems have been separately solved by the development of synchronised ventilation (Synchronised IPPV: SIPPV) and of the not-invasive ventilation, realised using nose cannulae in place of tracheal tube (Nasal IPPV: NIPPV).
SIPPV has been realised by the insertion of a small pneumotachograph between ventilation circuit and tracheal tube, i.e. an instrument able sensing inspiration flow caused by the spontaneous respiratory activity of the patient. Flow signal, as soon as intercepted, electronically determines the instantaneous activation of a mechanical cycle of the respirator (trigger system).
Application of this solution to the ventilation using nose-cannulae has not been possible until today, since presence of variable pressure leakages at the mouth (open or closed mouth) and nares level does not permit the use of flow signal for activation of trigger system. In fact, signal is unstable and with a too variable intensity to be suitably used by the trigger system presently known in the art.
On the other hand, lack of synchronism during nasal ventilation, besides having the side effects already described for IPPV, mainly determines a high variability of the treatment efficiency. In fact, not existing any more a closed system between ventilation circuit and aerial vie (tracheal tube), pressure wave generated by respirator is transmitted at the pulmonary level only if delivered during the patient spontaneous inspiration step, when glottides (phonatory cords) is physiologically dilated for easing the aerial flow. Delivering of a pressure during the patient spontaneous expiration step causes outlet of gas from the mouth and its by-pass at the gastric level, with the possibility of a dangerous abdominal distension. In order to realise newborn not-invasive synchronised ventilation (nSIPPV) it has then been used an “abdominal capsule”, instrument able detecting the increase of abdominal pressure following the diaphragm contraction, i.e. the main respiratory muscle. Said solution has soon presented remarkable limits due to the high number of false activations caused by spontaneous movements of patient not finalised to ventilation. This involves dangerous consequences, first of all the hyperventilation that can even cause cerebral damage in low weight new-borns.